A magnetic sensor can sense a change of the external magnetic field. A magnetic sensor can be used to detect rotation, angle, on/off state, position, presence, proximity, etc. There are many types of technologies that can be used to make a magnetic sensor such as Hall Effect, magnetoresistive, magnetoinductive, proton precession, optical pump, nuclear precession, and SQUID (superconducting quantum interference devices). Taking the magnetoresistive technology as an example, according to the magnetoresistive materials used, magnetic sensors can be categorized into anisotropic magnetoresistive material (AMR), giant magnetoresistive material (GMR) and tunneling magnetoresistive material (TMR) according to how they function and their sensitivities.
Most of these magnetic sensors are made as semiconductor devices, so their completion usually involves several steps: manufacturing from a substrate, wafer-level testing, singulation, packaging into individual chips and package-level testing. Wafer-level testing and package-level testing typically involve testing the functionality of devices such as memory cells and magnetic sensors formed in a wafer or a packaged integrated circuit (IC) with a tester comprising a testing interface. For magnetic sensors, wafer-level testing or package-level testing needs to generate an external magnetic field in order to test the performance of the magnetic sensors such as sensitivities in terms of different axes and accuracies in terms of different axies.